Schematic showing the emission geometry for a point on the hourglass wall. TT′ represents the tangent to the wall; ON is the normal to the wall. ﹩\overline{r}﹩ is the radially directed vector through the point. R is the radial distance to the point, ξ is the observed offset (§ 2.3), and ﹩\theta _{\mathrm{LOS}\,}﹩ and ﹩\theta _{\mathrm{star}\,}﹩ are as defined in the text (§ 3.2). The flux of ionizing photons incident on the wall is proportional to sin(θ_star). The emergent intensity is inversely proportional to sin(﹩\theta _{\mathrm{LOS}\,}﹩).